1. Field of the Invention
The present invention relates to an arrangement for the levitated guidance of a material web. The arrangement includes a plurality of nozzle boxes to which blowing air can be supplied. The nozzle boxes are arranged above and below the material web and are spaced apart from each other in travel direction of the material web. Each nozzle box has round blow nozzles which are arranged in rows of openings extending transversely of the travel direction of the material web and at the edges of the nozzle box. The blow jets emitted by the blow nozzles are inclined relative to the vertical longitudinal center planes of the nozzle boxes.
2. Description of the Related Art
The material webs in question are, for example, paper webs, such as wall paper, cardboard webs or strips of metal foil. The blowing air used for levitating the material web has several functions. On the one hand, the blowing air serves to guide the material webs without contact along the nozzle boxes. On the other hand, the blowing air serves to dry the material webs and to remove heat.
In an arrangement of the above-described type disclosed in DE-OS 16 29 029, the closed nozzle plate of each nozzle box is plane. Round blow nozzles are arranged in single rows adjacent the longitudinal edges of the nozzle box extending transversely of the travel direction of the material web. The axes of the round blow nozzles are inclined relative to the vertical longitudinal center plane of the nozzle box and intersect in an area on the side of the material web facing away from the nozzle plate. The round blow nozzles mounted in one row of openings are located in a transverse plane of the nozzle box in which the round blow nozzles of the other row of openings are also located.
This known arrangement has the disadvantage that it is comparatively difficult to manufacture because the round blow nozzles are arranged adjacent the longitudinal edges of the nozzle plates of the nozzle boxes. The known arrangement has the further significant disadvantage that the heat transfer conditions between the blowing air and the material web are not satisfactory. The reason for this disadvantage is the fact that the blowing air from the round blow nozzles is deflected at the material web almost completely at an acute angle against and in the travel direction of the material web. A space with pressurized air is formed between the material web, the nozzle plate and the blow jets. However, this pressurized air cannot result in an improvement of the heat transfer conditions.
Finally, particularly when the material webs are to be dried, unintended strips could be formed by the inclination of the axes of the round blow nozzles.